Description
The body of a mollusc is divided into three different region. The first of which is the head-foot. The head-foot is an elongated region with an anterior head and an elongate foot. The head contains a mouth and nervous and sensory structures. the elongate foot is used for attachment and locomotion. The second region is the visceral mass. The visceral mass is located dorsal to the foot and it has organs used for digestion, circulation, reproduction, and excretion. The last region is the mantle. The mantle tends to cover the whole body of the organism and it attaches to the visceral mass. The mantle is able to secrete a shell that covers the mantle, the shell has three layers. The three layers are the periostracum (outer layer), the prismatic (middle layer), and the nacreous (inner layer). The periostracum is a protein layer that gets secreted by cells at the mantles outer regions. The middle layer is the thickest layer and is composed of calcium carbonate mixed with organic materials. The middle layer is also secreted by cells at the mantle's outer margins. The inner layer is made of thin sheets of calcium carbonate along with organic materials. The inner layer is secreted by cells along the epithelial border of the mantle.
Another part of a molluscan is the mantle-cavity. The mantle-cavity is a space between the mantle and foot. The mantle serves to exchange gasses, excrete, eliminate digestive wastes, and release reproductive wastes. Another part would be the radula, a rasping structure in the mouth of a molluscs. The radula has a chitinous belt and rows of curved teeth. The radula lies above a structure called the odontophore. The odontophore is a fleshy tongue-like structure. Muscles near the odontophore help move the radula.